Every successful act of communication comes from the combination of the efforts of two parties: the speaker and the listener. The goal of the proposed research is to explore the division of labor between speaker and listener for the achievement of communicative success, by examining how speakers use syntactic flexibility- the ability to phrase the same idea in multiple ways -- to promote successful communication. For example, a speaker can optionally mention words like the complementizer that in sentences like The reporter heard (that) you committed a crime. Do speakers use syntactic flexibility in a comprehension-sensitive manner, choosing syntactic options that are especially easy to understand? Or do speakers instead focus on more speaker-centered pressures, creating sentences that are more quickly and efficiently produced? Accordingly, this research will investigate two kinds of factors that influence how speakers might use syntactic flexibility: comprehension-sensitive factors and speaker-centered factors. Three sets of experiments are proposed. The first two investigate possible comprehension-sensitive uses of syntactic flexibility. The first set explores whether syntactic flexibility is used to circumvent ambiguous or difficult garden path sentences or to avoid fully ambiguous sentences, under a variety of production circumstances. The second set explores whether speakers use flexibility to create preferred metrical structures, or to communicate discourse information. The final set explores the speaker-centered influences, including the kinds of retrieval difficulties that syntactic flexibility may be used to accommodate and the kinds of representations (syntactic or lexical) that underlie syntactic flexibility. These experiments, in addition to establishing how syntactic flexibility is used to achieve successful communication, will help to determine the nature of the language production mechanism that underlies normal and disordered language use, and are relevant to any field of application or research that involves the communication or transmission of information.